The present invention relates to a dynamic aortic patch for assisting cardiac function during a cardiac cycle of a patient when positioned with respect to an aorta of the patient, and in particular, to a dynamic aortic patch or blood pump with a reduced waist portion to reduce the probability of occluding an port to the inflatable chamber of the pump.
A dynamic aortic patch is permanently surgically implanted in the wall of the aorta to augment the pumping action of the heart. It is sometimes referred to as a mechanical auxiliary ventricle (MAV) or described as a permanent balloon pump.
Typically, the device includes a flexible bladder which is inflated and deflated in a predetermined synchronous pattern with respect to the diastole and systole of the patient to elevate aortic blood pressure immediately after aortic valve closure. Inflation and deflation of the bladder is accomplished by means of a supply tube connected to the bladder and to a percutaneous access device (PAD). The PAD is permanently surgically implanted in a patient""s body to provide a through-the-skin coupling for connecting the supply tube to an extra-corporeal fluid pressure source. Electrical leads from electrodes implanted in the myocardium are likewise brought out through the skin by means of the PAD. The xe2x80x9cRxe2x80x9d wave of the electrocardiograph can be employed to control the fluid pressure source to inflate and deflate the inflatable chamber in a predetermined synchronous relationship with the heart action.
The dynamic aortic patch acts to assist or augment the function of the left ventricle and is typically restricted to use in patients who have some functioning myocardium. The dynamic aortic patch does not need to be operated full-time, and in fact, is usually operated periodically on a scheduled on-time, off-time regimen. Typically, the patient can be at least temporarily independent of the device for periods of one to four hours or more, since the dynamic aortic patch does not require continuous operation.
The present invention is directed to an improvement over prior known dynamic aortic patches, for example as disclosed in U.S. Pat. No. 4,630,597. This patent discloses a device with an elongate bladder, where one longitudinal side is formed with a relatively thick, semi-rigid, inwardly concave wall. The semi-rigid wall is integrally joined to a relatively thin and flexible wall of the bladder. A layer is bonded to the outer side of the semi-rigid wall portion of the bladder and cut with a freely projecting peripheral edge portion to provide a suture flange for suturing the device in place within an incision in the aorta. A connecting tube is integrally formed on the semi-rigid wall portion and projects outwardly therefrom for connecting the lumen of the bladder to a pneumatic or other pressurized fluid supply source. The inner surface of the semi-rigid portion of the bladder is concave in shape and formed with a plurality of grooves extending from the supply tube opening outwardly to the periphery of the semi-rigid portion to prevent entrapment of air bubbles within the bladder as the bladder is being deflated.
It would be desirable to provide a dynamic aortic patch that did not require the formation of a plurality of grooves extending from the supply tube opening and outwardly toward the periphery. It would be desirable to provide a dynamic aortic patch that prevents, or reduces the possibility of, occluding the entrance to the inflatable chamber while deflating the chamber. It would be desirable to provide a dynamic aortic patch with a flexible membrane with different tension zones along its longitudinal length. It would be desirable to provide a dynamic aortic patch having a higher tension zone of the flexible membrane adjacent the opening of the passage into the inflatable chamber.
In the preferred embodiment of the present invention, the construction of a dynamic aortic blood pump or mechanical auxiliary ventricle (hereafter MAV) includes an elongate semi-rigid shell member having a concave inner surface and a flexible membrane integrally bonded to the outer peripheral surface of the shell member to define a chamber between the concave inner surface and the membrane. When the MAV is sutured into the descending aorta in the thoracic or abdominal cavity it will present an elongate elliptical septum (the membrane) which is caused to expand into the aorta under fluid pressure during an inflation cycle and displaces blood with an elongate semi-prolate spheroid bulging of the membrane projecting from the shell perimeter. In the deflation cycle the hydraulic (aortic blood) forces on the membrane typically cause the central portion of the membrane (the most supple region with the maximal aortic lumen intrusion) to collapse toward the shell concavity first. The fluid pressure inlet (outlet) tube leading to the internal passageway of the chamber is located centrally and could be prematurely occluded by the aforementioned membrane collapsibility (preventing full deflation). Prior devices, such as that disclosed in U.S. Pat. No. 4,630,597 disclose the use of a plurality of grooves that extend from the opening of the internal passage that prevent the passage from being prematurely occluded. Another prior known device disclosed in U.S. Pat. No. 4,051,841 teaches the use of a system of longitudinal filaments to prevent fluid entrapment under similar circumstances.
The pumping efficiency of the MAV is substantially reduced by this partial deflation, created when a portion of the air in the chamber is trapped by the premature occlusion of the inlet passage. The full stroke typical displacement capability of 35 cc (cubic centimeters) based on the membrane seating on the shell concavity would be reduced by the percentage volume of air entrapment were it not for the system of grooves that extended over the length of the MAV as disclosed in U.S. Pat. No. 4,630,597.
However, the system of grooves creates long term problems of membrane durability associated with the localized flexing of the membrane at each groove site, when it is hydraulically driven against the shell concavity (by aortic blood pressure) especially at high pulsing rates. The shell and membrane materials tend to be low slip, high grab substances that will create localized rubbing and heating along the groove ridges and when combined with the plurality of groove flexing and stretch sites can lead to membrane distortion and failure even in the presence of a surface lubricant. Furthermore, while the grooves prevent occlusion of the air outlet passage the grooves can create some delay in deflation by requiring exhausting air to travel through the long groove passageways formed if the membrane seats first in the central region of the shell concavity. A related problem concerns xe2x80x9cslappingxe2x80x9d or the thumping associating with the supple membrane being accelerated against the shell concavity.
The problems associated with occlusion prevention groove geometry in the MAV are eliminated by the present invention, which does not employ a groove system but makes use of preferential stretching modes built into the membrane geometry and which is conveniently referred to as a xe2x80x9cwaistxe2x80x9d. The waist consists of carefully graduated narrowing of the membrane mid-body that shortens the arcuate cord length so as to prevent the membrane from bottoming out against the shell concavity in the mid-zone of the MAV and thus permitting the unhindered exhausting of air from all of the MAV chamber. In this mode of operation occlusion of the air outlet is prevented, without resort to a groove system and its associated problems.
The MAV is essentially a bladder, and bladders along with elastomeric diaphragms find wide application outside of heart assist applications. Bladder and diaphragm devices are used as clamping and jacking or lifting devices as well as pumping and cushioning devices and as low pressure sensors. The problem of exhaust air entrapment is a universal one and the xe2x80x9cwaistxe2x80x9d concept is believed to be applicable especially for bladders of a longitudinal configuration which are in widespread usage.
A dynamic aortic patch or blood pump according to the present invention assists cardiac function during a cardiac cycle of a patient when positioned with respect to an aorta of the patient. The dynamic aortic patch or mechanical auxiliary ventricle includes an elongate semi-rigid shell having a contoured, concave inner surface terminating at a peripheral side edge. At least one passage extends through the shell to define an opening in the inner surface. A flexible membrane is continuously bonded to the shell adjacent the peripheral side edge to define an enclosed inflatable chamber in communication with the passage. The membrane has a reduced waist portion defining a membrane tension zone adjacent the opening of the passage into the chamber to prevent occluding the entrance while deflating the chamber.
The present invention also includes an apparatus for forming the flexible membrane for the dynamic aortic patch. The apparatus includes an elongate mandrel having a shape defined by substantially flat major surfaces opposite from one another and terminating at a rounded peripheral side edge extending between the major surfaces. The side edge is contoured and curved to define partial ellipses at both ends and a reduced waist portion adjacent a midway position. The mandrel is adapted to receive the thin, flexible, heat setable, membrane over one of the flat major surfaces and wrapped around the side edge a sufficient distance to form a flange adjacent to the opposite flat major surface. At least one clip can also be provided for holding the membrane in position during a heating process to set a defined shape into the memory of the membrane, where the shape corresponds to the shape of the mandrel.
A method of manufacturing a dynamic aortic patch according to the present invention includes the steps of providing an elongate mandrel having a shape defined by substantially flat major surfaces opposite one another and terminating at a rounded peripheral side edge extending between the major surfaces. The side edge is contoured and curved to define partial ellipses at both ends and a reduced waist portion adjacent a midway portion. The method also includes the step of placing a thin, flexible, heat setable membrane over one of the flat major surfaces and wrapping the membrane around the side edge a sufficient distance to form a flange adjacent the opposite flat major surface. At least one clip is provided for holding the membrane in place on the mandrel. The method includes the step of heating the membrane sufficiently to set the shape of the mandrel in the membrane. An elongate semi-rigid shell is provided having a contoured, concave inner surface terminating at a peripheral side edge and at least one passage extending through the shell to define an opening in the inner surface. The method also includes the step of permanently attaching the flange of the membrane to the shell adjacent the peripheral side edge to define an inflatable chamber in fluid communication with the at least one passage defining an opening in the inner surface of the shell.
Other objects, advantages and applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.